cxxflags =

rule cxx
  command = g++ $cxxflags -c -o $out $in

rule ld
  command = g++ $cxxflags $in -o $out

build build/huffman.o: cxx huffman.cpp | huffman.hpp
build build/grey.o: cxx grey.cpp | grey.hpp stb_image.h stb_image_write.h
build build/grey: ld main.cpp build/grey.o build/huffman.o

default build/grey